2 answers so far

I think to make it blue you have to dye it to a lighter shade before you dye it blue. That's with the safe ones anyway, there are some really powerful ones which would judt dye it straight away but they're so damaging to your hair.

Hey! I dyed my hair blue. My original hair colour is black. The only thing is that i had to bleach it first otherwise the colour wont show because your hair is too dark. Do you plan on dying all your hair bright blue? Perhaps get a blue hair spray and test it out first so you know for sure you like it. Then i would see a hairdresser and ask them about it. I didnt dye all my hair blue though.. So just see what a hairdresser has to say. You can always just do dip dye or dye the underneath part of your hair. Perhaps streaks. (: Hope this helped you and good luck!! (: x